Adapter API reference: signature change in a function (#5510)

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

src/content/docs/en/reference/adapter-reference.mdx

@@ -193,20 +193,18 @@ export function start(manifest) {
 
 The following methods are provided:
 
-##### `app.render(request, routeData, locals)`
+##### `app.render(request, { routeData, locals })`
 
 This method calls the Astro page that matches the request, renders it, and returns a Promise to a [Response](https://developer.mozilla.org/en-US/docs/Web/API/Response) object. This also works for API routes that do not render pages.
 
 ```js
 const response = await app.render(request);
 ```
 
-The method accepts a mandatory `request` argument, and two other optional arguments: [`routeData`](/en/reference/integrations-reference/#routedata-type-reference) and [`locals`](/en/reference/api-reference/#astrolocals).
+The method accepts a mandatory `request` argument, and an optional argument for [`routeData`](/en/reference/integrations-reference/#routedata-type-reference) and [`locals`](/en/reference/api-reference/#astrolocals).
 
 Provide a value for `routeData` if you already know the route to render. Doing so will bypass the internal call to [`app.match`](#appmatchrequest) to determine the route to render.
 
-When  used, `locals` must be the third argument passed. You can pass `undefined` for `routeData` if you are not targeting a specific route.
-
 The example below reads a header named `x-private-header`, attempts to parse it as an object and pass it to `locals`, which can then be passed to any [middleware function](/en/guides/middleware/).
 
 ```js
@@ -217,7 +215,7 @@ try {
         locals = JSON.parse(privateHeader);
     }
 } finally {
-    const response = await app.render(request, undefined, locals);
+    const response = await app.render(request, { locals });
 }
 ```